classic waka stream

柏木のもりの下草老いのよに
かかる思ひはあらじとぞ思ふ
Roma-ji

Kashiwagi no mori no shitagusa oi no yo ni kakaru omoi wa araji to zo omou

English Translation
Though the grass that grows
beneath the oak grove grows old
and a world grows old
such a thought will not arise
not ever, I think, in me
Meaning
Even in a world where the grass beneath the oak grove has grown old, no such thought will arise in me — that is what I think.
Commentary
21 The Grass Beneath the Grove

While the Lesser Captain of the Yoshimine family held the post of second officer in the Palace Guards, he was visiting the Lady of the Palace Guards. From her came "Kashiwagi no mori no shitagusa oinu tomo mi o itazura ni nasazu mo aranamu", and his reply was "Kashiwagi no mori no shitagusa oi no yo ni kakaru omoi wa araji to zo omou". The section closes with the exchange.
The Lesser Captain bore the Yoshimine surname, and this section is set during his term as second officer in the Palace Guards. The Lady of the Palace Guards appears repeatedly in this book: in the eighth section she exchanges poems with the Prince of the Ministry of Central Affairs, and in the tenth she composes a poem passing her former house. The same two appear again in the twenty-second section.
The setting is the same period of his visits.
What prompted the poem is the one she sent him, "Kashiwagi no mori no shitagusa oinu tomo mi o itazura ni nasazu mo aranamu", with its wish not to be cast aside.
This reply closes the twenty-first section. The prose passes no judgement; the section consists of the exchange alone.
This poem was later included in the Shokukokin-shū.

He sets her oak grove and its undergrowth in his own opening lines, starting the poem from her words. As an answering poem it is properly made.
The third line takes up her old age and turns it into a world grown old.
What he calls such a thought is the fear she has just voiced, that she might be cast aside; and the verb that follows denies it as something that will not come to be.
The closing phrase, with an emphatic particle governing the verb, pushes the judgement forward: this is what I think. Meeting the other's anxiety with a flat denial is the same posture as the exchange about the grass of forgetting in the sixteenth section.
Source
Yamato Monogatari
Other